util/gfx/wtk.c

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#include <stdint.h>
#include <stdlib.h>
#include <assert.h>
#include <membag.h>
#include <string.h>
#include "gfx/wtk.h"

uint8_t wtk_rescale_value(uint8_t value, uint8_t from_scale, uint8_t to_scale)
{
        uint16_t new_value;

        assert(to_scale > 0);
        assert(from_scale > 0);
        assert(value <= from_scale);

        new_value = value;
        new_value *= to_scale;
        new_value /= from_scale;

        return new_value;
}

void wtk_copy_string(char *dest, char const *source)
{
        assert(dest);
        assert(source);

        // Copy characters, including zero-terminator.
        while (*source != '\0') {
                *dest = *source;
                ++dest;
                ++source;
        }

        // Copy the terminating zero.
        *dest = *source;
}

void wtk_shade_pixel(gfx_color_t *pixel, uint8_t alpha)
{
        uint16_t green;
        uint16_t blue;
        uint16_t red;

        // Local workspace variables.
        gfx_color_t oldcol = *pixel;
        gfx_color_t newcol = 0x0000;

        // Split out red color, scale it, put into "newcol".
        red = oldcol & 0x00f8;
        red = (red * alpha) + red;
        red >>= 8;
        red &= 0x00f8;
        newcol |= red;

        // Split out green color, scale it, put into "newcol".
        green = ((oldcol << 3) | (oldcol >> 13)) & 0x003f;
        green = (green * alpha) + green;
        green >>= 8;
        green = (green << 13) | (green >> 3);
        newcol |= green;

        // Split out blue color, scale it, put into "newcol".
        blue = (oldcol >> 8) & 0x001f;
        blue = (blue * alpha) + blue;
        blue &= 0xff00;
        newcol |= blue;

        // Write back result.
        *pixel = newcol;
}

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